Series offset capacitor for internal reference based capacitive sampling

Abstract

A system and method for reducing the power required for a capacitive sensing measurement and for simplifying a sample capacitor signal offset while reducing charge injection during synchronous rectification by enabling the touch sensor to begin a measurement cycle at an arbitrary voltage rather than forcing the touch sensor to have a precise known voltage.

What is claimed is: 
     
         1 . A method for reducing power consumption of a capacitive sensing touch sensor, said method comprising:
 providing a plurality of electrodes disposed in an orthogonal and co-planar array of two sets of electrodes, wherein the two sets of electrodes always perform different functions from each other, switching between a drive function and a sense function;   providing a touch controller that transmits drive signals to the plurality of electrodes and which receives sense signals from the plurality of electrodes, wherein the touch controller includes a signal sampling circuit for receiving the sense signals;   initializing the signal sampling circuit by enabling the signal sampling circuit to use an arbitrary voltage that is present on the signal sampling circuit before receiving the sense signals;   receiving the sense signals by the signal sampling circuit; and   determining a position of at least one object in contact with the plurality of electrodes using the sense signals.   
     
     
         2 . The method as defined in  claim 1  wherein the step of initializing the signal sampling circuit further comprises not forcing the signal sampling circuit to a predetermined voltage, and thereby reducing power consumption by saving current that would otherwise be used by the signal sampling circuit to reach the predetermined voltage. 
     
     
         3 . The method as defined in  claim 2  wherein the step of initializing the signal sampling circuit further comprises reducing a set-up time for the signal sampling circuit to prepare for receiving the sense signals because the signal sampling circuit does not have to be forced to the predetermined voltage. 
     
     
         4 . The method as defined in  claim 2  wherein the method further comprises reducing components in the signal sampling circuit by eliminating circuitry that was used to drive the signal sampling circuit to the predefined voltage. 
     
     
         5 . A method for simplifying a capacitive sensing touch sensor, said method comprising:
 providing a plurality of electrodes disposed in an orthogonal and co-planar array of two sets of electrodes, wherein the two sets of electrodes always perform different functions from each other, switching between a drive function and a sense function;   providing a touch controller that transmits drive signals to the plurality of electrodes that are functioning as drive electrodes and which receives sense signals from the plurality of electrodes that are functioning as sense electrodes, wherein the touch controller includes a signal sampling circuit for receiving the sense signals;   initializing the signal sampling circuit by enabling the signal sampling circuit to use an arbitrary voltage that is present on the signal sampling circuit before receiving the sense signals;   receiving the sense signals by the signal sampling circuit; and   determining a position of at least one object on the plurality of electrodes using the sense signals.   
     
     
         6 . The method as defined in  claim 5  wherein the step of initializing the signal sampling circuit further comprises not forcing the signal sampling circuit to a predetermined voltage, and thereby reducing power consumption by saving current that would otherwise be used by the signal sampling circuit to reach the predetermined voltage. 
     
     
         7 . The method as defined in  claim 6  wherein the step of initializing the signal sampling circuit further comprises reducing a set-up time for the signal sampling circuit to prepare for receiving the sense signals because the signal sampling circuit does not have to be forced to the predetermined voltage.